Power amplification (PA) is a significant portion of power consumption in wireless transceivers. Next generation mobile wireless communication systems require both high power and high efficiency power amplifiers to provide good communication quality and long battery life. Some designs for high efficiency and high power PAs are known to the art, and many of the amplifiers are implemented based on Class-E and Class-F amplifier topologies. Modern bandwidth-efficient communication signals usually have high peak-to-average ratios (PARs), which makes the PA operate with significant power back-offs. For example, most of the 4G systems are based on orthogonal frequency-division multiplexing (OFDM) signals, which include multiple independent carriers where each carrier transports parallel data. For 54 Mbps 64-QAM signal of IEEE 802.11g WLAN is composed by 48 carrier signals and four pilot signals with PAR of over 10 dB. Existing amplifier designs that are configured for these applications require extra circuits, such as envelope amplifier for dynamic biasing and an additional peak PA for the Doherty topology, which introduce additional losses, size issues, and increase the complexity of the entire circuit. Comparatively, dynamic load modulation (DLM) is a known method for improving the efficiency at power back-offs. DLM utilizes tunable output matching networks (OMNs) with passive tuning components which do not consume DC power and can be designed as a part of the OMN.
Five characteristics are desired for power amplifiers in high-frequency applications: high power (typically >1 W), high peak efficiency (>60%), broad bandwidth (up to one octave), high linearity, and efficiency enhancement at power back-offs (>30% at 6 dB back-off). Neither the existing fixed-frequency nor tunable power amplifier designs that are known to the art meet all four of the desired characteristics simultaneously. Consequently, improvements to amplifiers that enable high power output, high efficiency, wide band tunability with strong linearity, and high efficiency in power back-off situations would be beneficial.